In humans, sleep spindles are 10- to 16-Hz oscillations lasting approximately 0.5–2 s. Spindles, along with cortical slow oscillations, may facilitate memory consolidation by enabling synaptic plasticity. Early recordings of spindles at the scalp found anterior channels had overall slower frequency than central-posterior channels. This robust, topographical finding led to dichotomizing spindles as "slow" versus "fast," modeled as two distinct spindle generators in frontal versus posterior cortex. Using a large dataset of intracranial stereoelectroencephalographic (sEEG) recordings from 20 patients (13 female, 7 male) and 365 bipolar recordings, we show that the difference in spindle frequency between frontal and parietal channels is comparable to the variability in spindle frequency within the course of individual spindles, across different spindles recorded by a given site, and across sites within a given region. Thus, fast and slow spindles only capture average differences that obscure a much larger underlying overlap in frequency. Furthermore, differences in mean frequency are only one of several ways that spindles differ. For example, compared with parietal, frontal spindles are smaller, tend to occur after parietal when both are engaged, and show a larger decrease in frequency within-spindles. However, frontal and parietal spindles are similar in being longer, less variable, and more widespread than occipital, temporal, and Rolandic spindles. These characteristics are accentuated in spindles which are highly phase-locked to posterior hippocampal spindles. We propose that rather than a strict parietal-fast/frontal-slow dichotomy, spindles differ continuously and quasi-independently in multiple dimensions, with variability due about equally to within-spindle, within-region, and between-region factors.

SIGNIFICANCE STATEMENT Sleep spindles are 10- to 16-Hz neural oscillations generated by cortico-thalamic circuits that promote memory consolidation. Spindles are often dichotomized into slow-anterior and fast-posterior categories for cognitive and clinical studies. Here, we show that the anterior-posterior difference in spindle frequency is comparable to that observed between different cycles of individual spindles, between spindles from a given site, or from different sites within a region. Further, we show that spindles vary on other dimensions such as duration, amplitude, spread, primacy and consistency, and that these multiple dimensions vary continuously and largely independently across cortical regions. These findings suggest that multiple continuous variables rather than a strict frequency dichotomy may be more useful biomarkers for memory consolidation or psychiatric disorders.

对于人类来说，睡眠纺锤波是 10 至 16 Hz 的振荡，持续约 0.5-2 秒。纺锤体与皮质缓慢振荡一起，可以通过实现突触可塑性来促进记忆巩固。头皮纺锤体的早期记录发现，前通道的频率总体低于中央后通道。这一强有力的拓扑发现导致将纺锤体分为“慢”和“快”，建模为额叶皮层和后皮层的两个不同的纺锤体发生器。使用来自 20 名患者（13 名女性，7 名男性）的颅内立体脑电图 (sEEG) 记录和 365 个双极记录的大型数据集，我们表明额叶通道和顶叶通道之间的纺锤波频率差异与病程内纺锤波频率的变异性相当单个纺锤体、跨给定站点记录的不同纺锤体以及跨给定区域内的站点。因此，快速和慢速主轴仅捕获平均差异，从而掩盖了频率上更大的潜在重叠。此外，平均频率的差异只是主轴不同的几种方式之一。例如，与顶叶相比，额叶纺锤体较小，当两者都参与时，往往出现在顶叶之后，并且显示纺锤体内频率的较大下降。然而，额叶和顶叶纺锤体的相似之处在于，它们比枕叶纺锤体、颞叶纺锤体和罗兰纺锤体更长、变化更小、分布更广泛。这些特征在与后海马纺锤体高度锁相的纺锤体中得到强化。我们提出，纺锤体在多个维度上连续且准独立地变化，而不是严格的顶叶快/额叶慢二分法，其变异性几乎同样地归因于纺锤体内、区域内和区域间因素。

意义陈述睡眠纺锤波是由皮质丘脑回路产生的 10 至 16 Hz 神经振荡，可促进记忆巩固。在认知和临床研究中，纺锤体通常分为慢前和快后类别。在这里，我们表明纺锤体频率的前后差异与单个纺锤体的不同周期之间、来自给定部位的纺锤体之间或来自区域内不同部位的纺锤体之间观察到的差异相当。此外，我们还表明，纺锤体在其他维度上有所不同，例如持续时间、幅度、传播、首要性和一致性，并且这些多个维度在皮质区域中连续且很大程度上独立地变化。这些发现表明，多个连续变量而不是严格的频率二分法可能是记忆巩固或精神疾病更有用的生物标志物。